Study of physical properties of Cs₂TlGaX₆ (X = Cl, Br) halide perovskites via HSE-06 hybrid technique for high efficiency solar cells

Double perovskite halides Cs₂TlGaCl₆ and Cs₂TlGaBr₆ are promising for photovoltaic applications due to their optoelectronic properties. The first-principles density functional theory (DFT) with the HSE06 hybrid functional was applied to systematically investigate their structural stability, electronic structure, optical absorption, and mechanical properties. The calculated tolerance and octahedral factors confirm stable crystal structures. The indirect band gaps of 2.50 eV (Cs₂TlGaCl₆) and 1.54 eV (Cs₂TlGaBr₆) are suitable for visible-light harvesting. Strong visible-light absorption and low reflectivity are observed. Elastic constant calculations based on the Voigt–Reuss–Hill approximation validate mechanical stability. The Spectroscopic Limited Maximum Efficiency (SLME) estimates promising photovoltaic efficiencies of 12.41% for Cs₂TlGaCl₆ and 29.73% for Cs₂TlGaBr₆ perovskite. These findings highlight the potential of Cs₂TlGaCl₆ and Cs₂TlGaBr₆ for low-cost, high-efficiency solar cells, warranting further experimental investigations.